1. Field of the Invention
The present invention relates to a vertical heat treatment apparatus and a method for cooling the apparatus, and more particularly to a vertical heat treatment apparatus and a method for cooling the apparatus, which can cool the space between a furnace body and a treatment container with high precision.
2. Description of the Related Art
In the manufacturing of a semiconductor device, various types of vertical heat treatment apparatuses are used to perform various treatments, such as oxidation, diffusion, CVD (chemical vapor deposition), etc., of a semiconductor wafer as a processing object. A common vertical heat treatment apparatus comprises a heat treatment furnace including a treatment container for housing and heat treating a semiconductor wafer, and a furnace body, disposed such that it surrounds the treatment container, for heating the wafer in the treatment container. The furnace body includes a cylindrical heat insulator, and a heat generating resistor provided in the inner circumferential surface of the heat insulator via a support.
In the case of a heat treatment apparatus capable of batch-wise treatment, for example, a spiral heater element (also called heater wire or heat generating resistor) disposed along the inner wall surface of a cylindrical heat insulator may be used as the above-described heat generating resistor. Such a heater element can heat the interior of a furnace at a high temperature, e.g. about 500 to 1000° C. A cylindrical ceramic insulator, obtained by firing a heat insulating material such as ceramic fibers, can be used as the above-described heat insulator. Such a heat insulator can reduce the amount of heat that may be lost through heat radiation or conduction, thus enhancing the efficiency of heating. The above-described support may be made of a ceramic material, and may support the heater element at a given pitch in such a manner as to allow thermal expansion and contraction of the heater element.
For the above-described vertical heat treatment apparatus, a method has been developed in which after heating a wafer at a high temperature, the space between the furnace body and the treatment container is rapidly cooled in order to streamline a heat treatment operation while maintaining the accuracy of heat treatment for the wafer.
In carrying out the rapid cooling method in the vertical heat treatment apparatus, when the pressure in the space between the furnace body and the treatment container is a positive pressure, hot air will blow out of the furnace body, which can cause breakage of the furnace body itself or its peripheral devices. When the pressure in the space between the furnace body and the treatment container is a highly negative pressure, on the other hand, the heat insulator of the furnace body can break. Further, the external air will enter the furnace body, which may result in a non-uniform temperature distribution in the interior of the treatment container and, in addition, can cause local breakage of the heat generating resistor.
It is, therefore, necessary to keep the space between the furnace body and the treatment container at a slightly negative pressure in carrying out the rapid cooling method in the vertical heat treatment apparatus. However, no method has yet been developed which can keep the space between the furnace body and the treatment container at a slightly negative pressure securely with high precision.